This invention relates generally to tone generation in electronic musical instruments and more particularly to the generation of a suitable tonal waveform and/or envelope for generated tones in such an instrument. This disclosure will address the problems of envelope production specifically, although the invention is applicable to generation of both waveforms and envelopes.
A major area of endeavor in the electronic musical instrument arts has been to develop electronic systems for simulating the overall tonal quality and response characteristics of conventional musical instruments. Because of the time-varying and complex waveforms and envelope characteristics of the tones associated with many musical instruments, it has heretofore been difficult or impossible, either from a technical or financial standpoint, to generate electronically the requisite signals to simulate such waveforms and envelope characteristics to any degree of accuracy.
For example, a conventional piano produces a tone having an envelope characteristic which very rapidly reaches a peak or maximum intensity and thereafter decays at a predetermined or inherent rate, either naturally after an extended time period or upon release of a key which causes a damper to engage and stop the vibrating piano wire. Similarly, with other instruments, there is generally an attack and decay envelope characteristic associated with the instrument, which is often relatively difficult to accurately reproduce electronically.
Notwithstanding the foregoing difficulties, many attempts to electronically generate such tonal envelopes have been made with varying degrees of success. The prevalent approach of prior art devices has been to employ various forms of capacitor charge and discharge circuits. The generally exponential discharge characteristics of capacitors simulate a typical percussion voice decay characteristic (e.g., of a piano) closely enough so as not to be audibly objectionable. This characteristic may not be suitable, however, for simulating other instruments, e.g., strings or wind instruments. This then leaves the problem of providing some means responsive to the intensity of player actuation (e.g., in a keyboard instrument, the intensity with which the player depresses a key) to produce a suitable signal corresponding to the peak or maximum level of the envelope, to insure a signal of proper over-all amplitude level or "scale". In the prior art this has commonly been accomplished by some sort of electromechanical transducer responsive to each tone initiating actuation of the player. In the case of a keyboard instrument this requires such a transducer associated with each key of the keyboard. One such electromechanical transducer is shown, for example, in Gschwandtner, U.S. Pat. No. 3,588,310. Other arrangements of the prior art have made use of multiple capacitor charging and discharging circuits in combination with suitable gating elements to simulate percussion (e.g. piano) envelope characteristics. Such a system is shown, for example, in Machanian et al. U.S. Pat. No. 3,935,783.
While the systems and devices of the above-mentioned prior art patents have proven useful for their stated purposes, the present invention improves upon these systems by providing both a high degree of accuracy in reproduction of envelope waveshapes of conventional musical instruments and ability to generate a plurality of different such envelope waveshapes.
With the advent of relatively inexpensive and flexible digital electronic circuits and particularly the availability of low cost large scale integrated circuits and the technique for their design and manufacture, other approaches to this problem have become feasible. For example, Wheelwright et al, U.S. Pat. No. 4,067,253, shows one form of tone generating system, specifically designed for simulating an instrument of the percussion type (e.g. a piano). This patent shows a system which makes use of digital processing techniques and digital electronic circuits to a certain extent. It is the intent of the present invention to utilize digital processing techniques and digital electronic circuits to an even greater extent and in doing so, to present a significant improvement over the prior art.
The present invention involves the use of digital processing techniques and digital electronic circuit design, as mentioned, to provide an envelope generation system that may advantageously be realized as a single large scale integrated circuit chip. This integrated circuit chip accommodates a plurality of individual and independent tone signal initiation means as imputs. For example, in the case of a keyboard instrument, a plurality of keys thereof are accommodated. The invention includes an independent envelope generator for each tone initiating means (e.g. key) responsive to that tone initiating means and in particular to the force (velocity) with which the tone initiating means is struck. The envelope generators of the invention are further individually controllable as to the exact relation of their output signals (envelope waveform) to the force or velocity with which the key or other tone initiating means is initiated, and also as to the shape of the envelope waveform generated thereby. Advantageously, therefore, the invention is unexpectedly flexible, being able to generate virtually any desired envelope shape.